Automatic one-star tracking navigation device



R. E. JASPERSON 3,194,949

AUTOMATIC ONE-STAR TRACKING NAVIGATION DEVICE 2 Sheets-Sheet 1 ALTITUDE(h) DIFFERENTIATOR DIFFERENTIATOR ALTITUDE (l1) ALTITUDE SIGNALGENERATOR VERTICAL STABI LIZER N T v 2 m m Ddk'L .m m .l W N Wh T O D LL T M D I E M5 S Rm 0 UA l 0?! 2 0 D n 6 T T u m 5 U 5 W 2 c N N v w m w2 2 n n .N m I T n g 3 m mm u m mm 2 T A A w INVENTOR ROBERT E.JASPERSON AGENT July 13, 1965 Filed May 8, 1961 0 M H TO wm 1+ E MS30|\\E I 3 2 ww HR A 2 w R n L 05 2 mw n p H 2 3 RH C T 2 2 AM 5- M W OTWO W0 0 AUTOMATIC ONE-STAR TRACKING NAVIGATION DEVICE Filed May 8, 1961July 13, 1965 R. E. JASPERSON 2 Sheets-Sheet 2 LHA 50 E.-

J g H FIG. 2

o M H n 2 INVENTOR ROBE/P T JA SPERSON ATTORNEYS AGENT United StatesPatent 3,194,949 AUTOMATEC ONE-STAR TRACKING NAVIGATION DEVICE Robert E.Jasperson, Ferry Farms, Annapolis, Md. Filed May 8, 1961, Ser. No.108,681 6.Claims. (Cl. 235-151) (Granted under Title 35, US. Code(1952), see. 266) light conditions when it is impossible or diflicult toreference the system on celestial bodies because of the effects andinterference of the sun. Instead of trying to overcome this interferencethis system is designed to take advantage of these effects. This is doneby a one-startracking system which is adapted to track on the sun duringthe daylight hours and to track another celestial body when the sun isobscured by the earth.

One object of this invention is to provide a one-startrackingnavigational device which will track continuously over a twenty-fourhour period and will in turn convert the tracking information intotrigonometric form and combineand convert this information into positiondata and conrtol information for guiding the vehicle.

Another object of this invention is to provide a one-startrackingnavigation device that determines position from following the sun.

Another object of this invention is to provide a one-startrackingnavigation device having a stabilized platform to hold the trackerstable with relation to earth.

Another object of this system is to provide a daylight hours,sun-tracking navigation device for determining geographic position.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same become better understood byreference to the following detailed description when considered inconnection with the accompanying drawings wherein:

FIG. 1 illustrates the operative system of the embodiment of theinvention;

FIGS. 2 and 3 are diagramsto facilitate the explanation of the system.

In the embodiment of the invention illustrated in FIG. 1, anastro-tracker 1 is mounted for suitable rotation and movement on astabilized platform 2. The astro-tracker may take any one of severalconventional forms and therefore it has been illustrated in diagrammaticform to facilitate the description of the invention.

The platform is stabilized by a suitable rotating means which is adaptedto determine the true vertical to the earth. The means used in theillustrated device operates on the same principle as a radiometricsextant which scans the periphery of the sun to determine the locationof the center. In the invention, the radiometric sextant is adapted toscan the periphery of the earth by detecting the absorbed or reflectedenergy and in this way the true vertical to the earth can be determinedto a high degree of accuracy. This in turn overcomes certain limitationsfound in using a pendulum effect. An imaginary line drawn between thecenter of the earth and the space vehicle then becomes the true verticaland the plane of the 3,194,949 Patented July 13, 1965 stabilizedplatform upon which the astro-sextant 1 may be mounted is maintainednormal to this line.

The astro-tracker 1 may be of the type which has a sensing area 3 at therear of the tube 5 which may be divided into four equal segments. Eachof these segments has a separate radiation sensing area diametricallyopposite each other. The astro-tracker 1 is designed in such a mannerthat an image of the celestial body being tracked is focused on thesensing area 3 of the tube 5. When the astro-tracker 1 is positioned onthe center of the star, the amount of radiation on each of the foursensing areas 3 is equal and four equal signals are sent to trackerposition control 19 over the leads 21. Since the signals are equal, nocontrol signal is derived from the tracker position control 19. But asthe celestial body and the vehicle move with relation to each other theimage at the rear of the tube 3 deviates from the balance position. Anunbalanced signal is sent to the tracker position control 19 by means ofthe leads 21 and control signals are sent over the leads 22 and 23 tothe altitude servo 30 or the azimuth servo 50 respectively. When theastro-tracker l is again focused on the celestial body the detectors arebalanced and the position control signal is cut off and theastro-tracker continues in this direction until further deviation isdetected.

As can be seen from FIG. 1 the altitude serve 30 drives a worm gear 31which coacts with arcuate gear 4 on the astro tracker 1. The other endof the worm gear 31 is attached to a shaft position signal generator 32which may be an extremely accurate selsyn. The output of this signalgenerator 32 is connected to the correction computer which providescompensation for the coriolis eifec of the earths rotation. Coriolisacceleration is a function of true air speed, latitude, and the relativehearing of the starbeing observed. The computer 70 also provides for acorrection due to the eifects of refraction and instrument errors. Thecorrected altitude signals h is transferred to the differentiator 20 bymeans of the lead 72.

A space reference element is rigidly secured to the vertical stabilizer8t) and the stabilized platform 2.

In this manner any deviation of the platform is readily detected by thereference element 100. The space reference element is designed tofulfill two functions: to provide positional information (latitude andlongitude), and to serve as an invariant reference point against whichto measure the rate of change of the bearing of a selected celestialbody. The concept is somewhat analogous to a means for indicating time,such as a chronorneter or electric clock. A time instrument must firstbe set by reference to some independent source; e.g., a time signal oranother time piece. In the event of an interruption in power such as arun down spring or power failure the time piece must be re-energized andre-set. By the same principle the space reference element 1% must beoriented initially with reference to known positional data or byastronomical observations and data.

If power is interrupted the reference element 108 loses track of itsposition and has to be reset. This resetting is done by theastro-tracker 1 and the related components.

One form of space reference element could be a zeror:If.ewa.mnimntnnuttlntllmlllllllllll 9 divider circuit 14 by theconductors 216 and 21$. divider 14 operates on the signals dh a? This onthe lead 251.. computer 4%.

This function is operated on by the The value of the declination d isput into the computer unit as by means of conductor 25.2.

The particular computer unit 40 forms no part of the invention and tofacilitate the explanation of the device it has been shown in blockform. The computer could be any device designed by conventionalprograming techniques for the purpose of solving a problem or group offunctions. Any number of advanced programing manuals will explain theprocess involved. The computer unit also has the latitude and longitudedestinations programed into it by means of the input leads 253 and 254respectively.

An autopilot 61 is connected to computer unit 40 by conductors 255 and256. This autopilot 61 will control the flight of the vehicle over thepredetermined course and distance in response to the command signal fromthe computer unit 40.

The visual latitude display 90 and longitude display 911 are connectedto the computer unit 4t? by conductors 257 and 258 respectively andfunction in accordance with the information signals from the computer49.

A conventional visual display compass 51 is also connected to thecomputer unit 4% by a conductor 259. The compass 51 also operates as anerror checker by comparing the azimuth signal Z, which is obtained fromcomputer 4h, with the signal of the azimuth signal generator M. Theusual displays of compass heading, and the visual latitude and longitudedisplays primarily serve as an information aid to the pilot.

In operation, the astro-tracker 1 will track on a single star and moreparticularly the star would be the sun. For this reason the operation ofthe navigational tracking device will be explained in relation to thesun.

As an illustration, consider the relative motion of the sun and theearth. The sun appears to rise in the east, transits a local meridian,reaches a maximum altitude, then sinks in the west as viewed from apoint on earth.

When the observer is north of the sun, it will appear on the left (east)and at first will apparently increase in altitude very rapidly while thehorizontal component or azimuth appears to move very slowly to theright. As the sun approaches the meridian the altitude will increasemore slowly while the azimuth will increase more rapidly. When the sunis at the meridian the apparent rate of change in altitude is zero andthe rate of change of the azimuth is at a maximum. As the sun starts tosink, the rate of decrease in altitude becomes more rapid and reaches amaximum when the sun sets. The rate of change of the azimuth goes from amaximum to a minimum during the period of setting.

In practice the astro-tracker would be aligned with the sun eitherautomatically or manually when it is sufficiently above the horizon togive an accurate reading. The motors would bring the astro-trackcr 1into approximately the correct center alignmcnt with the sun. From thisdiscussion it is seen that the approximate value of Z is and theaproximate value of h is O.

The signals from astro-tracker 1 would cause the control circuit 2th tospeed up or slow down the servos 3t and 59 until a null was reached.This is known as aided tracking. The altitude increase approximatelysinusoidally and the altitude servo 30 would receive signals constantlybut in minute increments (0.1 min. of arc). The azimuth servo 59 wouldreceive similar signals. This ould happen throughout the day if the sunwas obscured momentarily the tracker 1 would continue at the lastdesignated rate.

The diiterentiators 2t) and 26 then convert the rate signal from thecorrection computer 741 and the sensitive reference element 1%. Theoutputs from these differentiators are divided by circuit 14 to obtainthe function dlz/dZ. The altitude signal It and the function dh/dZ areoperated on by the multiplier 15 to obtain the function:

dh (1) tan M see (it) where:

M=position angle of body) h=altitude Z=azimuth D :decli-nation Given thevalue of altitude h, declination D and angle M the computer unit 4% cansolve for latitude and longitude by the following formulas:

(2) sin (lat.)=sin ([1) sin (D)|cos (/1) cos (D) cos (M) (3) sin (t):sin (M) cos (it) sec (lat) long.=tiG.H.A. (From Air Almanac)G.H.A.=GREENWICH HOUR ANGLE (4) sin (Zn) =sin (t) cos (D) sec (/2)Zn=azimuth angle The method of finding position from the formulas is asfollows: From a fixed position Z in latitude 57 N. the altitude h of thesun will be set at 38 00.7 and the azimuth (Zn) will be 114 when itsdeclination d is 20 N. and its local hour angle (Ll-IA) is 50 E. asshown in FIG. 2.

The rate of change of altitude over an interval of 8 minutes of timewill be 7.46 per minute and the rate of change of the azimuth From avehicle at point Z on course 40 and at a speed of 420 knots (FIG. 3) atthe same instant as above,

' the rate-of-change of the relative altitude of the sun due tovehicular motion will be:

523 1.9295' 60 cos 74 -7(0.27564) 19295 25112 cos 24 min.

Since the earth rotates to the east at the rate of 15'/min. the totalrate-of-change of the azimuth may be found from the equation:

dZ 15+VesecL (15+3.878 19509 EZ-15.17(15 15.17

The ratio of V dh dZ dh 9.39

min.

The combined rate-of-change of the suns altitude will be:

cos 60 7 (0.5)

2 L 1 I H (it 35* min.

The velocity of the vehicle east with respect to the sun is equal to:

3.5 10f23 cos 70 min. and 5'6 dZ 1510.23 sec 57 dt 15 min.

The ratio:

dh f7 0.12500 In the astronomical triangle the position angle (M) maythen be determined from the equations:

sin M=sin (t) cos (L) sec (h) or dh tan M= sec (h) In the first exampleof a sun position above:

sin M=sin 50 cos 57 sec 3800'.7

tan M:(0.49182) (1.2692) In the second example given above:

sin M=sin 13 cos 57 sec 5l46'.l

tan M=(0.125) (1.616)

The remaining elements of the astronomical triangle may be obtained inaccordance with the following equations:

sin (lat.)=sin (h) sin (d)+cos (h) cos (d) cos (M) sin (2) =sin M cos(11) sec (lat) LONGITUDE=G.H.A.:t sin Zn=sin (t) cos (d) sec (11) Theseequations would be solved automatically and the desired informationobtained in the manner as previously described.

It Will be understood that various changes in the details, materials,steps and arrangements of parts, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art Within the principle and scope of theinvention as expressed in the appended claims.

What is claimed as:

1. A navigation device comprising a stabilized platform, an astrotracker connected to said stabilized platform, control means connectedto said *astro-tracker being adapted to follow one star, signal meansconnected to said astro-tracker for determining the altitude of thestar, and means responsive to the altitude of the star for determining.the geographic position of said stabilized latform.

2. An automatic one-star-tracking navigation device comprising, astabilized platform, a radiometric sextant which is adapted to scan theperiphery of the earth, said radiometric sextant being operativelyconnected to orient said stabilized platform normal to a vertical axisoriginat ing at the center of the earth, an astro-tracker connected tosaid platform, control means connected to said astrotracker, saidcontrol means adapted for controlling the position of said astro-trackerto continually follow the sun, first signal means, said first signalmeans being connected to said astro-tracker control means to generate asignal corresponding to the altitude of the sun relative to thestabilized platform, second signal means connected to saidastro-traclrer to indicate horizontal movement of the astro-tracker Withreference to the stabilized platform, a space reference elementconnected to said stabilized platform and said astro-tracker :to detectdeviation of the astro-tracker from a redetermined vertical bearingplane and to detect deviation of the stabilized platform from apredetermined reference point in space, a correction computer connectedto the first signal means adapted to correct the altitude signal, firstand second dif ferentiator means, said first difierentiat-or beingconnected to said correction computer to differentiate the correctedaltitude signal, said second ditterentiator being connected to saidspace reference element to difierentiate the bearing signal, a dividerconnected to said ditferentiators to divide the derivative of thebearing signal by the derivative of the corrected altitude signal, amultiplier con nected to said divider and said correction computer tooperate on the corrected altitude signal and the quotient of thederivative signals, a computer unit, a source of declination signals,said computer unit being connected to said source of declinationsignals, said multiplier and said correction computer, said computerunit being adapted to control an autopilot, and a geographic positiondisplay, a compass connected to said computer unit and said secondsignal means, said compass being adapted to detect error between thehorizontal movement signal of the astro-tracker and an azimuth sign-a1generated by the computer unit.

3. An automatic one-star tracking navigation device comprising:

an astro-tracker;

control means to position the tracker With relation to a singlecelestial body;

signal generating means connected to said control means to indicate theangular position of the astro-tr-acker;

means to differentiate the angular position signal;

stabilizing means connected to said a-stro-tracker;

and

computin means responsive to the angular position signal and itsderivative to determine the geographic means to differentiate the signalrepresentative of the angular position of the optical tracker;

means to differentiate the bearing signal;

means connected to the difierentiators to provide a signalrepresentative of the quotient of the two derivatives; and

means responsive to the angular position signal and to the quotient ofthe derivatives to provide a trigonometric function thereof.

position of the system. 10 6. The system of claim 5 further includingvertical 4. An automatic one-star tracking navigation device stabilizingmeans connected to the stable platform comcomprising: prising astabilized platform; rotating means including a radiometric sextant foran astro-tracker mounted on the platform; determining a vertical axis tothe center of the earth; feedback means to control the astro-tracker tocon- 15 and 'tinuously follow a single celestial body; means connectedto the astro-tracker to provide a signal representative of the angularposition of the astro-tracker relative to th plane of the stableplatform; and 20 means responsive to the angular position of theastroiineans to orient the stable platform normal to the vertical axis.

Referen es Cited by the Examiner UNITED STATES PATENTS tracker f prviding the geographic position of the 3 33%; 522 platform. i 5- Thesystem Of claim 4 further including 2,921,757 1/60 e 244l4 a spacereference element connected to th tabl plat- 25 3,048,352 8/ 62 nsen250-203 form to provide a signal representative of the bearing celestialbody being tracked; and

wherein the means for providing the geographic position of the platformincludes MALCOLM A. MORRISON, Primary Examiner.

WALTER W. BURNS, 521., Examiner.

1. A NAVIGATION DEVICE COMPRISING A STABILIZED PLATFORM, ANASTRO-TRACKER CONNECTED TO SAID STABILIZED PLATFORM, CONTROL MEANSCONNECTED TO SAID ASTRO-TRCKER BEING ADAPTED TO FOLLOW ONE STAR, SIGNALMEANS CONNECTED TO SAID ASTRO-TRACKER FOR DETERMINING THE ALTITUDE OFTHE STAR, AND MEANS RESPONSIVE TO THE ALTITUDE OF THE STAR FORDETERMINING THE GEOGRAPHIC POSITION OF SAID STABILIZED PLATFORM.